There is a high incidence and prevalence of mental health problems among young people, with several barriers to help-seeking noted in this group. High rates of mental health problems have also been reported in children and adults on the autism spectrum. Taken together, young autistic people may be a particularly vulnerable group when it comes to mental health. Yet, there has been remarkably little work on the mental health needs and experiences of young autistic adults (16–25 years). Adopting a community-based participatory research (CBPR) approach – in which academic researchers and young autistic adults collaborated in an equitable research partnership – we explored young autistic people’s experiences of mental health problems and their perspectives on the support they sought, if any, for these problems. A total of 130 young autistic adults took part in the research: 109 completed an online survey and 21 took part in detailed interviews. The results highlight how young autistic people find it difficult to evaluate their mental health, experience high levels of stigma and often face severe obstacles when trying to access mental health support. The findings also demonstrate how listening to – and learning from – young autistic people is crucial in ensuring that their mental health needs are met.